No, its is most certainly not a reliable guide!
Well, according to the WTBTS it's not, anyway.
Back in my witnessy days, the public talk entitled: "Is your conscience a reliable guide for living?" majored on Man's totally inability to do anything remotely good of his own accord. Man was not to be trusted at all, every act and thought needed to be supplied to him from the Bible, and, of course, the Faithful and Discrete Slave. Do not trust yourself, young man, you are not to be trusted!
Hmm. That little bit of negative imprinting stayed to haunt me personally for many years, so, like many dubs and ex-dubs, a vague generalised sense of guilt was my constant companion, with the result that my life was inflicted with an uneasy sense of malaise for much of the time. (It's because you have turned your back on Jehovah..whisper whisper...) However...
I will state what I now believe to be the case, if this thread runs. First off, some people need to tell me if they do believe that one's conscience is a reliable guide to life.
Or not!
Englishman.